Thin autofocus camera module by a large-stroke micromachined deformable mirror

Abstract

The conventional auto-focus and zoom image systems were made by a set of motor-moved lenses. Because of mechanical moving parts, it is not easy to miniaturize their sizes. In this paper, we propose a thin autofocus system using a large stroke MEMS (micro-electro-mechanical systems) deformable mirror which has the potential to downscale the size and to minimize chromatic aberration. The large stroke MEMS deformable mirror is made by a polyimide membrane that has a maximum 12 microm displacement over a 3 mm aperture. The module size is 5.4 mm thick in optical design layout and 6.7 mm after packaging. This autofocus system is designed with the f-number=4.13, on-axis MTF=0.28 at full frequency of 230 cycles/mm, and incident light within+/-26 degree. The position of clear image can vary from 4 cm to 50 cm achieved by controlling the surface curvature of the MEMS deformable mirror.

Continuous optical zoom module based on two deformable mirrors for mobile device applications

“…Structure of MEMS deformable mirror and the way to tune focal length: (a) without electrostatic force (b) actuated with electrostatic force. [5] The surface profile of the actuated MEMS deformable can be approximate as spherical surface [5]. The diopter of MEMS deformable mirror is given by…”

“…Snap-down effect occurs when the center displacement of the membrane becomes too large that it touches bottom electrode. The results are showed as following figures 2 [5]. …”

“…The usage of deformable mirrors in imaging systems has the potential of inducing low chromatic aberrations and reducing thickness of imaging devices. The autofocus lenses based on DMs have been demonstrated in the previous work [5]. The application of DM results in a compact and good image quality autofocus camera design.…”

Polymorphic optical zoom with MEMS DMs

“…A general conclusion that can be drawn from this body of work is that when high-numerical apertures and off-axis beam paths are combined with active optics in an imaging system, the resulting images are often degraded by aberrations. Such aberrations have been characterized and found to be substantial for a number of specific active focusing configurations [10,17,18] . Recently, two systems with aberrationcompensated optics were reported for active focusing [17] and active zoom [19] .…”

“…Such aberrations have been characterized and found to be substantial for a number of specific active focusing configurations [10,17,18] . Recently, two systems with aberrationcompensated optics were reported for active focusing [17] and active zoom [19] . One, developed at National Taiwan University, described a prototype autofocus module for consumer cameras that featured a MEMS DM and a rigid aspheric mirror that was intended to compensate expected off-axis aberrations.…”